The row units of spindle-type cotton picker harvesters typically contain rotating vertically-oriented drums having multiple rows of rotating knurled (or barbed) conical spindles which, as the harvester moves along the row of cotton plants, contact the open bolls to extract the seed cotton, winding the cotton fibers onto the spindles, which are then unspooled by a rotating drum consisting of a stack of doffing discs which are configured to wipe (or doff) the seed cotton from the spindles, after which the cotton fiber is then collected by a vacuum system for further processing. The doffing discs consist of a circular base on which multiple resilient raised lugs are formed, the lugs arranged circumferentially on one side of the doffing disc, with each lug having a flat doffing face parallel to the base. Multiple doffing discs are mounted on a vertical shaft, and are spaced apart either by separate spacers which are adjacently mounted on the shaft between the doffing discs, or by integral spacers which are part of the doffing discs.
The doffing discs are oriented on the vertical shaft with their lug side downwards, and the height of the doffing discs is adjusted such that the flat doffing faces of the lugs graze the top of the spindles as they rotate past, unwinding the cotton fibers from the base of the conical spindle to the tip. The lugs of existing doffer discs have a symmetric, generally trapezoidal, profile when viewed along the radius of the disc, with the leading and trailing sides of the lugs being sloped between the doffing face and the base. Having this sloped configuration on the leading side of the lug can result in seed cotton being forced down between the spindle and the doffing face of the lug, where it places upwards force on the doffer disc and downward force on the spindle, resulting in increased stress and wear on the doffer lugs and spindle, leading to vibration and “rounding off” of the leading edge of the doffer lug, producing inefficient doffing.
Doffer discs are typically manufactured from a resilient material like rubber, or now more often polyurethane elastomer, which is formed around a supporting loop or hub of rigid material, usually metal. Conventional doffer discs which lack integrated spacers, such as are used in John Deere cotton pickers, are formed around a flat metal disk, or loop, which has a central hole for mounting the doffer disc on the vertical shaft. In addition to serving as a mounting point, the metal loop is held in compression between the adjacent spacers, and provides internal support to the resilient base and lugs of the doffer disc. The stress on the doffer disc caused by seed cotton being forced between the doffing face of the lug and the spindle by the sloped leading side of the doffer lug, as described above, can also cause momentary flexing of the metal loop, which can result in vibration and increased wear of the doffer disc and the lugs. A need therefore exists for improved doffer discs that provide reduced vibration, increased wear resistance, and more efficient doffing.